1. Field of the Invention
The present invention relates generally to an electrical capacitor of stacked dielectric layers with metal coatings between the layers and, more specifically, to an end face arrangement on the dielectric layer stack.
2. Description of the Prior Art
The subject matter of U.S. Pat. No. 4,563,724 is an electrical capacitor composed of a consolidated stack of dielectric layers layered one on top of another. Each dielectric layer is provided with a metal coating wherein alternating ones of the coatings extend to the ends of alternating ones of two projections which are formed by an incision which proceeds in the direction of the thickness of the stack and roughly in the center of one side thereof. The end surfaces of the projections in the consolidated stack are provided with metal contact layers, which connect the antipolar metal coatings to one another. The capacitor includes the following features:
(a) the dielectric layers of the capacitor are composed of plastic films; PA1 (b) the coatings are composed of regenerably thin layers of valve metal and cover one surface of each dielectric layer practically up to the edges of the longitudinal sides as well as up to both sides of the projections and, if need be, up to the edge of the upper narrow side of the stack which lies opposite the narrow side containing the incision; PA1 (c) alternating from dielectric layer to dielectric layer, one of each of the two projections are provided with metal-free insulating strips, whereby the depth of the incision is greater than the width of the remaining metal strip and, preferably, coincides with the inside edges of the insulating strips or extends beyond these edges into the stack; and PA1 (d) the metal layers connecting the antipolar coatings to one another at the projection end surfaces are manufactured by means of metal spraying. PA1 (e) as a consequence of wavy cut edges in the manufacture of the dielectric bands, the ends of the projections of the respectively first dielectric layers comprise wave hills and wave valleys; whereas the ends of the projections of the respectively second dielectric layers are limited by smooth cut edges; PA1 (f) the dielectric layers are laterally offset relative to one another by such an amount that the smooth cut edges of the second dielectric layers at the projection ends are located roughly in the center between the wave hills and the wave valleys of the first dielectric layers; and PA1 (g) at the upper, narrow side of the stack, both the first dielectric layers as well as the second dielectric layers have smooth cut edges. PA1 (a) metallized tapes are wound onto a drum, the metallized tapes potentially including continuous, metal-free strips at one edge each, whereas intermittent metal-free insulating strips in the winding direction are generated in the regions of the opposite edges and at spaces therefrom. The intermittent insulating strips are generated prior to winding such that the insulating strips, when the tapes are wound onto the drum, lie in a plane perpendicular to the winding axis and so that each end of each of the insulating strips extend into or proceed slightly beyond a region where the incision will later lie; PA1 (b) during winding onto the drum, the tapes are guided such that the centers of the insulating strips of the upper tape are symmetrically arranged over the centers of the spaces between the insulating strips of the lower tape in the finished mother capacitor; PA1 (c) after the winding and consolidation of the original, or primitive, capacitors or, respectively, mother capacitors, at least the end face formed by the edges is provided with a metal layer by means of metal spraying while still on the drum; PA1 (d) after the division into individual mother capacitors, incisions are produced perpendicular to the winding direction in the center between two adjacent cut lines, so that the two projections are formed at each capacitor depending upon the basis of the width and depth of these incisions; PA1 (e) severing the individual capacitors, if need be after fastening the power leads, by sawing along cut lines which proceed through the centers of the insulating strips; and PA1 (f) completion of the capacitors by applying cap-shaped power leads or other power leads insofar as these have not already been secured in method step (e). PA1 (a) metallized tapes are wound onto the drum, these metallized tapes being provided with intermittent metal-free insulating strips in the winding direction at both edges and at intervals therefrom, being provided therewith before or during winding such that the insulating strips lie in a plane perpendicular to the winding axis while being wound onto the drum and both the ends as well as the beginnings of the insulating strips project into the region of the later incision or proceed slightly beyond this region; PA1 (b) during winding onto the drum, the tapes are guided such that the centers of the insulating strips of the upper tape are arranged symmetrically over the centers of the spaces between the insulating strips of the lower tape in the finished mother capacitor; PA1 (c) after the winding and consolidation of the original, or primitive, capacitors or, respectively, the mother capacitors, metal layers are applied by metal spraying to both end faces formed by the edges while still on the drum; PA1 (d) after the division into individual mother capacitors, incisions are generated at both sides perpendicular to the winding direction in the center between two respective cut lines, the two projections arising on the basis of the width and depth of these incisions; PA1 (e) severing the individual capacitors, if need be after securing power leads, by sawing both along cut lines which proceed through the centers of the insulating strips as well as along a cut line which lies parallel to the edges in the center of the mother capacitor; and PA1 (f) completion of the capacitors by applying cap-shaped power leads or other power leads insofar as these have not already been secured in method step (e).
GB Pat. No. 811,983 discloses forming an irregular surface on the end of a capacitor roll including rolling the capacitor of a strip with irregular or wavy edges to provide secure adhesion of the sprayed metal contacts. Such round windings are adequately stable in and of themselves and do not entail the same manufacturing problems as in the manufacture of stack capacitors. Other non-uniform capacitor edges are shown in EP-Al 0 011 033 and in German Pat. No. 24 16 566.
Additional features of the U.S. Pat. No. 4,563,724 capacitor will be set forth in conjunction with the following section describing the present invention.